Implantable medical devices such as pacemakers, defibrillators, neuro-stimulators, and the like are generally deployed in a housing comprising two metal halves forming a “clam shell” assembly. Electrical communication to external sensing electrodes and/or therapy delivery electrodes is often accomplished by means of a rigid plastic connecting module fixed to an outer portion of the housing. One or more feed-through connectors permit electrical communication to and from the electrical components or circuitry contained within the housing while at the same time maintaining the hermeticity of the device.
The construction of such implantable medical devices using the above described basic architecture oftentimes requires complex manufacturing operations which increase costs, lower yields, and limit design freedom. One such operation includes providing the electrical contacts and interconnections between components such as batteries, capacitors, and feed-throughs with internally deployed hybrid circuitry formed on substrates such as printed wiring boards (PWBs), flex substrates, ceramic substrates, and the like. That is, the substrates are not directly compatible with welding or wire-bonding. In the case of welding the substrate metalization and even the substrate itself may be damaged due to their respective low melting points. For example, in the case of a PWB or flex substrate, the epoxy glass or polyimide would melt if an attempt were made to weld directly to the plated metal. Ceramic substrates may also be damaged by the rapid local heating. While wire-bonding to the metalization of a PWB or flex circuit is possible, a gold finish is required and solder splatter is possible. Furthermore, the use of a gold finish can cause brittle solder joints.
It is well known that the trend towards smaller device sizes requires smaller and more closely spaced interconnect terminals. Unfortunately, this presents certain problems. First, components can “swim” or “float” on solder pads during the soldering process resulting in non-uniform component spacing and excessive tilting with respect to the PWB surface. This variation must be kept to a minimum to achieve minimum electrical separation and bond/weld variations induced by the angle of their terminal bond/weld surface. Additionally, as the size of the individual terminals or contacts continues to shrink, the terminals are difficult to manage with current pick-and-place surface-mount assembly equipment.
One approach currently being used involves the soldering of individual, gold-plated terminal blocks to the hybrid substrate. Electrical coupling to these blocks is then made by welding or wire-bonding. In addition, the use of individually placed surface-mount solder buttons is known. These approaches, however, still suffer from the above described disadvantages. The use of a ceramic block array provides for multiple connections to a hybrid circuit with consistent terminal spacing and protection from solder wicking to the bond surface; i.e. solder migrating up the side, and in some cases to the top. Unfortunately, the impedance through each terminal from one surface to the other surface results in large voltage drops at high currents.
In view of the forgoing, it should be appreciated that it would desirable to provide a surface-mount solderable terminal assembly that provides weldable and/or wire bondable surfaces for electrically connecting the components of a hybrid circuit to other components such as batteries, capacitors, feed-throughs, etc. which is cost effective and which provides for reduced spacing between contacts while at the same time avoiding the disadvantages and problems described above. Additional desirable features will become apparent to one skilled in the art from the foregoing background of the invention and following detailed description of a preferred exemplary embodiment and appended claims.